The present invention relates to a method for the substantially complete removal of water from surfaces of various articles. The problem of the water removal from manufactured articles is particularly felt in the field of electronics, fine mechanics and finishing of precious metals.
From patent application EP 826,714 in the name of the Applicant compositions are known formed by a (per)fluoropolyether having number average molecular weight in the range 300-1,500 and by a fluorinated non ionic additive which can have both end groups of oxyethylene type or one end group of oxyethylene type and the other of fluorinated or perfluorinated type; in the additive structure the ratio by weight (K) between (per)fluorinated part and hydrogenated part being in the range 1.50-3.50. In the examples an additive is used having a perfluorinated end group and as perfluoropolyether solvent a compound of formula:
CF3O(C3F6O)1,7(CF2O)0,1CF3 
having molecular weight of about 450. The results obtained in the Examples are extremely good and effective in the removal of water from surfaces of various articles. However the additives having perfluorinated end groups are obtained by a particularly expensive process.
The need was felt to have available additives having a fluorinated end group able to give the same removal efficiency of additive with perfluorinated end group. In fact the additives having fluorinated end groups can be produced with an industrial process having higher yields and therefore more advantageous from an industrial point of view. The Applicant has verified that repeating the Examples of said patent application with additives having a fluorinated instead of a perfluorinated end group, the water is removed from the substratum in a less effective extent than using the same additive having the perfluorinated end group. See the comparative Examples.
There was therefore the need to find compositions, containing a perfluoropolyether solvent and an additive with a fluorinated end group, to make possible the water removal from the substratum in a likewise effective way than using the additive with the perfuorinated end group.
An object of the present invention is a method for removing water from surfaces of various articles, comprising the steps of covering said surface with a composition having a specific weight higher than that of the water and subsequently removing water from the composition by skimming, wherein a composition consisting essentially of the following components is used:
A) a non ionic additive having a fluoropolyether structure with a fluorinated T end group containing one chlorine atom, having the following formula:
T-ORf(CFY)-Lxe2x80x83xe2x80x83(I) 
wherein
L=Xxe2x80x94CH2CH2(OCH2CH2)nBxe2x80x83xe2x80x83(Ia) 
wherein:
X=CH2O; CH2NRxe2x80x3; CONRxe2x80x3; CH2OCH2CH2NRxe2x80x3; CH2OCOCH2O;
B=OH; SH; NHRxe2x80x3; OCH3; OCOCH3,
with Rxe2x80x3=H; C1-3 alkyl,
T is a fluorinated radical selected from ClCF2CF(CF3)xe2x80x94, CF3CFClCF2xe2x80x94, ClCF2CF2xe2x80x94, ClCF2xe2x80x94,
Y=CF3 or F,
the radical Rf being of (per)fluoropolyether type;
being in said additive of formula (I):
the number average molecular weight of the fluoroether part T-ORfxe2x80x94 in the range 400-2,000,
the ratio by weight (K) between the fluorinated part and the hydrogenated L part of the additive is in the range 1.50-4.00; the n parameter in formula (Ia) being such as to meet said ratio;
B) a perfluoropolyether having number average molecular weight in the range 300-900,
the ratio KI between the number average molecular weight of the fluoropolyether part T-ORfxe2x80x94 of the additive and the number average molecular weight of component B) being higher than 1.60.
The number average molecular weight of the fluoroether part T-ORfxe2x80x94 of the compounds of formula (I) component A) is preferably in the range 500-1,200, still more preferably in the range 600-1,000.
The perfluoropolyether component B) has number average molecular weight preferably in the range 300-650.
The radical Rf of (per)fluoropolyether type preferably comprises repeating units statistically distributed along the polymer chain selected from: (CF2CF2O), (CFYO) wherein Y is equal to F or CF3, (C3F6O); (CF2(CF2)zO) wherein z is an integer equal to 2 or 3; (CF2CF(ORfxe2x80x2)O), (CF(ORfxe2x80x2)O) wherein Rf, is equal to xe2x80x94CF3, xe2x80x94C2F5 xe2x80x94C3F7; CR4R5CF2CF2O wherein R4 and R5 are equal to or different from each other and selected between Cl or perfluoroalkyl, for example having 1-4 carbon atoms.
If the ratio KI is lower than or equal to 1.60 (see the comparative Examples) the composition containing the additive does not result effective in the substantially complete removal of water. This was not inferable from EP 826,714; in fact in the Examples of this patent application the ratio KI calculated between the molecular weight of the fluorinated part of the additive and the molecular weight of component B) is 1,46 and therefore lower than the limit that the Applicant has unexpectedly found for the use according to the method of the present invention of the additives component A) having a fluorinated end group containing one chlorine atom.
To obtain a composition to be used in the method according to the present invention it is further necessary that the ratio K between the fluorinated part and the hydrogenated part of the additive lies within the above limits.
When the ratio K is outside the above limits the additive is not effective in the substantial removal of water from the substratum.
The following (per)fluoropolyether Rf which comprise the following repeating units can in particular be mentioned as the preferred ones:
(a) xe2x80x94(CF2CF(CF3)O)a(CFYO)bxe2x80x94
wherein Y is F or CF3; a and b are integers such that the molecular weight is in the above range; a/b is in the range 10-100;
(b) xe2x80x94(CF2CF2O)c(CF2O)d(CF2(CF2)zO)hxe2x80x94
wherein c, d and h are integers such that the molecular weight is within the above range; c/d is in the range 0.1-10; h/(c+d) is in the range 0-0.05, z has the above value, h can be equal to 0;
(c) xe2x80x94(CF2CF(CF3)O)e(CF2CF2O)f(CFYO)gxe2x80x94
wherein Y is F or CF3; e, f, g are integers such that the molecular weight is within the above range; e/(f+g) is in the range 0.1-10, f/g is in the range 2-10;
(d) xe2x80x94(CF2O)j(CF2CF(ORfxe2x80x3)O)k(CF(ORfxe2x80x3)O)lxe2x80x94
wherein: Rfxe2x80x3 is xe2x80x94CF3, xe2x80x94C2F5, xe2x80x94C3F7; j,k,l are integers such that the molecular weight is within the above range; k+l and j+k+l are at least equal to 2, k/(j+l) is in the range 0.01-1,000, l/j is in the range 0.01 and 100;
(e) xe2x80x94(CF2(CF2)zO)sxe2x80x94
wherein s is an integer such as to give the above molecular weight, z has the already defined meaning;
(f) xe2x80x94(CR4R5CF2CF2O)j 
wherein R4 and R5 are equal to or different from each other and selected from H, Cl or perfluoroalkyl, for example having 1-4 carbon atoms, jxe2x80x2 being an integer such that the molecular weight is the above mentioned one;
(g) xe2x80x94(CF(CF3)CF2O)jxe2x80x3xe2x80x94
jxe2x80x2 being an integer such to give the above molecular weight.
These structures comprising the mentioned repeating units and the methods for their preparation are described in patent GB 1,104,482, in U.S. Pat. No. 3,242,218, U.S. Pat. No. 3,665,041, U.S. Pat. No. 3,715,378, U.S. Pat. No. 3,665,041, EP 148,482, U.S. Pat. No. 4,523,039, U.S. Pat. No. 5,144,092, and for the functional derivatives see U.S. Pat. No. 3,810,874. All these patents are herein incorporated by reference.
The value KI is preferably higher than 2.00 and still more preferably in the range 2.00-3.00.
The perfluoropolyether component B) preferably has the following structure:
Txe2x80x2xe2x80x94Oxe2x80x94Rf-Txe2x80x3
wherein:
Rf has the above meaning;
Txe2x80x2 and Txe2x80x3, equal or different, are selected from xe2x80x94CF3, xe2x80x94C2F5, xe2x80x94C3F7.
Particularly preferred structures are the following:
Txe2x80x2O(C3F6O)axe2x80x3(CFYO)bxe2x80x3Txe2x80x3xe2x80x83xe2x80x83(III) 
wherein Y=F or CF3, axe2x80x3 and bxe2x80x3 are integers such that the molecular weight is within the indicated range with axe2x80x3/bxe2x80x3 in the range 1-40; Txe2x80x2 and Txe2x80x3 are as above defined.
Txe2x80x2O(C2F4O)p(CF2O)qTxe2x80x3xe2x80x83xe2x80x83(IV) 
wherein p and q are integers such that the molecular weight is within the indicated range with p/q in the range 0.6-1.2; Txe2x80x2 and Txe2x80x3 are as above.
Txe2x80x2O(C3F6O)sxe2x80x2Txe2x80x3xe2x80x83xe2x80x83(V) 
wherein sxe2x80x2 is an integer such that the molecular weight is within the indicated range; Txe2x80x2 and Txe2x80x3 are as above.
The extreme effectiveness of the compositions of the invention containing the perfluoropolyether component B) and the fluorinated non ionic additive component A) allows to use reduced amounts of additive, generally lower than or equal to 0.1% by weight, preferably lower than 0.05% with respect to the total weight of the composition.
The additives A) of the present invention and the compositions containing the additives A) and the component B) are new products and allow to obtain the above results when they are used in the removal of water from the subtratum. They allow to obtain the unexpected result to have a complete or substantially complete removal of water from the substratum. The compositions of the invention are easily removable from the substratum without leaving any residue using the conventional methods used for substrata (semiconductors).
To prepare the monofunctional additives having a COF end group the above mentioned patents can be used, for example starting from a monofunctional (per)fluoropolyether, i.e. having xe2x80x94COF end groups, following the disclosure of U.S. Pat. No. 3,810,874, herein incorporated by reference.
For example for preparing additives wherein X=CH2O and B=OH one starts from the product having a xe2x80x94COF end group. The xe2x80x94COF group is reduced by metal hydrides to give the alcoholic derivative xe2x80x94CH2OH, which by reaction with one mole of ethylene oxide gives the monoaddition product xe2x80x94CH2Oxe2x80x94CH2CH2OH. The corresponding tosyl derivative is prepared by reaction with the paratoluensulphonic acid chloride. The tosyl derivative is reacted with a large excess of a polyethylenglycol in the presence of potassium terbutylate. When X takes the other above values, the disclosure of the above U.S. Pat. No. 3,810,874 is followed.
The following Examples have an illustrative and not limitative purpose of the scope of the present invention.
Experimental Part
The used perfluoropolyether solvents B) are commercially available and are different by the number average molecular weight, and consequently they have different boiling point and viscosity.
The water removal has been determined according to the following method:
a distilled water drop (about 0.1 ml) is deposited on a flat surface of a glass crystallizer having a base area of about 10 cm2. Then some ml of the tested solution containing 0.03% by weight of additives are added along the walls until covering the drop and after 30xe2x80x3 how the removal of water from the flat crystallizer surface has taken place, is observed. The attributed points correspond to the following cases:
1 Complete removal
2 Drop residue  less than 10%
3 Drop residue  greater than 10%
4 No removal
The 1 and 2 values are considered acceptable (substantially complete removal).